Conventionally, a plurality of roofing materials are laid on a roof bed in longitudinal and lateral directions, thereby a roof being formed. In this case, the roofing materials adjacent to each other in the lateral direction (a direction orthogonal to a water-flow direction of the roof) are laid so as to be shifted from each other by a predetermined length in the lateral direction and be overlapped to each other in an up and down direction, and attempt to secure waterproof of the roof after construction (for example, see Patent Literature 1). Specifically, as shown in FIG. 6, an approximately planar cover part 40 is formed at one side end part of a roofing material A, and a sacrificed part 41 has an approximately waved cross section and is formed at the other side end part of the roofing material A. The sacrificed part 41 of the roofing material A laid on the roof bed 6 is covered with the cover part 40 of the other roofing material A. Therefore, the two roofing materials A and A are attempted to be laid adjacent to each other in the lateral direction.